This invention is in the area of improved fire retardants that include guanylurea phosphate [(H2Nxe2x80x94C(NH)xe2x80x94NHxe2x80x94C(O)xe2x80x94NH2).H3PO4] (GUP) and boric acid, to materials, including wood and composite wood products that include these fire retardants, and to methods of making and using same.
Wood products, especially wood products used in the building construction industry, are commonly treated with chemical fire retardants that reduce the inherent ability of the wood to catch fire and combust. Many of these fire retardants contain acidic components which, when exposed to high heat, are activated and catalyze the dehydration of cellulose. This reaction converts the cellulose in the wood into water and char, and reduces the susceptibility of the wood to continuous combustion. Because these acid-based fire retardants decompose the wood in order to prevent combustion, it is important to prevent premature activation of the acid components. This is especially true for building products that are used to construct roofs, because of the extremely hot temperatures that these materials experience.
Many fire retardant chemical treatments for wood have been based on amine-phosphorus compounds.
For example, Goldstein et al., U.S. Pat. No. 2,917,408 disclose the preparation of fire retardant wood with a combination of dicyandiamide (H2Nxe2x80x94C(NH)xe2x80x94NHxe2x80x94CN) and phosphoric acid (H3PO4). Goldstein et al., U.S. Pat. No. 3,159,503 disclose the preparation of fire retardant wood with a combination of dicyandiamide, phosphoric acid and very small amounts of formaldehyde. In addition, Juneja, U.S. Pat. No. 3,832,316 discloses a composition for imparting fire retardancy to wood comprising dicyandiamide, melamine, formaldehyde, and phosphoric acid and suggests that minor amounts of other materials may be substituted for some of the phosphoric acid, such as boric acid. Juneja, Canadian Pat. No. 917,334 discloses a composition for treating wood to impart fire retardancy, in which the composition comprises dicyandiamide, urea, formaldehyde and phosphoric acid. The document suggests that minor amounts of other materials may be substituted for some of the phosphoric acid, such as boric acid. Other similar patents include U.S. Pat. Nos. 2,935,471; 3,137,607; 3,874,990 and 4,010,296.
While most of the above described chemical compositions based on dicyandiamide, melamine, urea, formaldehyde and phosphoric acid are effective for imparting fire retardancy to wood, they suffer from one or more drawbacks. Compositions containing solids of more than about 15 percent urea render the wood hygroscopic. Further, compositions that contain formaldehyde tend to be resinous and require high drying temperatures of about 100xc2x0 C. to 110xc2x0 C. to completely cure the resin, thereby impairing the strength of the wood.
U.S. Pat. No. 4,373,010 to Oberley (the Oberley ""010 patent) reported that the aforesaid disadvantages could be obviated, and that a superior fire retardant could be formed, by partially reacting water, phosphoric acid, dicyandiamide and boric acid. The Oberley ""010 patent describes several liquid fire retardants that contain guanylurea phosphate (GUP) and boric acid, and several methods for preparing the GUP/boric acid retardants. The retardants preferably contain about 70 weight parts of GUP and about 30 weight parts of boric acid. Dicyandiamide and phosphoric acid are mixed at a 1:1 molar ratio to produce the GUP.
In a preferred method, Oberley ""010 reacts dicyandiamide with phosphoric acid for 35 to 45 minutes in water to form guanylurea phosphate (GUP), in a solution that contains 50-70 percent solids. The reaction is only allowed to proceed to about 80-95 percent completion, in order to prevent the formation of insoluble precipitates. Boric acid is then mixed with the GUP solution, and the mixture cooled to ambient temperature and diluted to from 3 to 18 percent solids.
In one example, Oberley ""010 formed a 15 percent aqueous treating solution from dicyandiamide, phosphoric acid and boric acid (DPB) in a ratio of 70 percent combined dicyandiamide and phosphoric acid to 30 percent boric acid. While agitating, the dicyandiamide was charged to a glass reaction flask, followed by the water and phosphoric acid. The mixture was then heated to 80xc2x0 C. over a period of 20 minutes and maintained at that temperature for 3xc2xd hours. The boric acid was then added and the solution cooled to room temperature over a period of 30 minutes. The resultant solution comprised principally guanylurea phosphate, unreacted dicyandiamide and phosphoric acid of about 10 percent of the original amount, and boric acid.
In another method disclosed in the Oberley ""010 patent, dicyandiamide, phosphoric acid, and boric acid are initially heated together. The patent does not give any further details about this process, except to indicate that the method is prone to yield aqueous mixtures with insoluble precipitates, especially at high solids concentrations of from 50 to 80 percent.
At least one other method, that is not disclosed in the Oberley ""010 patent, is used commercially to prepare a GUP/boric acid fire retardant. This method is used to produce solid GUP/boric acid fire retardants that are bagged and sold in large super sacks for pressure treatment of wood products. To use the solid material, pressure treaters pour the contents of the bag into a large vat of heated pressure treating solution, and allow the solids to dissolve before using the solution in their pressure treating operation.
These commercially available solid GUP/boric acid fire retardants are sold in large super sacks of chunks that are 0.5-1.5 inches in size. The solids contain boric acid and GUP, and result from a reaction that gives about 90% yield, and are typically sold. When a wood pressure treater receives a super sack of solid GUP/boric acid fire retardant, he dissolves the entire bag in water for use in his pressure treatment process.
The GUP/boric acid fire retardants disclosed and used in the prior art suffer from a number of disadvantages. First and foremost, the process for making the fire retardants wastes a considerable amount of raw materials. In the commercial process discussed above, about 10% of the dicyandiamide and phosphoric acid raw materials is wasted because the reaction only proceeds to about 90% of its theoretical yield. Oberley ""010 intentionally wastes a considerable amount of raw materials by preventing more than 80-95% conversion of dicyandiamide and phosphoric acid into GUP. As a result, the pressure treater ends up with raw materials and intermediates from the GUP production process in his wood products.
The GUP/boric acid fire retardants of the prior art also contain unwanted by-products from the GUP production process. One of these by-products is seen when a solution of the fire retardant is subjected to potentiometric titration, because it produces an equivalence point at pKa 3.2. It is believed that this by-product is a salt of dicyandiamide and phosphoric acid. A purer product that did not contain such by-products and unreacted raw materials would be desirable from a quality point of view.
The solid GUP/boric acid fire retardants that are sold commercially also suffer from a number of distinct disadvantages. For example, they are presently sold in super sacks and are very difficult to manage by the wood treater, because they frequently harden during transport in the bag, and an entire bag of the material must be added to a pressure treating solution in order to assure adequate and proportional mixing between the GUP and boric acid. A homogenous blend of solids would reduce the packaging that is needed when a customer needs a smaller portion of material than present in a super sack, because a homogenous blend would allow customers to use only a portion of the retardant in the super sack packaging (as opposed to having to dissolve an entire super sack).
The liquid fire retardants disclosed in Oberley ""010 similarly suffer from several distinct disadvantages, especially related to transportation of the materials. In order to prevent the formation of undesirable precipitates during transport, the liquid fire retardants disclosed in Oberley ""010 must be continuously heated during transport and/or diluted to unsatisfactory low levels.
The GUP/boric acid fire retardants disclosed and used in the prior art also do not meet the needs of the manufacturers of oriented strand board (OSB) and other composite wood products. Methods for producing composite wood products such as oriented strand board are known. In general, particles of wood of various sizes and geometrical configurations are consolidated using various glue or binder mixes such as isocyanate, urea formaldehyde, phenol formaldehyde, melamine formaldehyde, acid phenol resins, etc., under heat and pressure. Typical processes are described in U.S. Pat. No. 2,642,371 issued Jun. 23, 1953, to Fahrni, and U.S. Pat. No. 2,686,143, issued Aug. 10, 1954, to Fahrni. The particles of wood chips, strands, fibers, or other cellulosic material, are typically referred to as the furnish.
There are several methods currently used to impart fire retardance to composite wood products. U.S. Pat. No. 4,163,820 reports that, as then practiced, most methods for imparting flame-retardance to wood particleboard involve the treatment of the wood chips used with an aqueous fire-retardant solution, followed by chip drying and finally chip gluing and particleboard consolidation. The patent also reports that other methods wherein the wood chips are dusted with solid frame-retardant additive are also practiced although less actively.
U.S. Pat. No. 4,039,645 reports that it is known in the art to use borates in the production of composite wood products. One method used is to treat the green chips with Na2B8O13.4H2O, either in solution or as a dry powder. It is then conventional to add powdered boric acid, H3BO3, into the resin mix prior to using the resin mix to consolidate the treated wood chips. The addition of the boric acid to the glue mix is required since all sodium borates such as Na2B8O13.4H2O have a relatively high pH which interferes with the binding of resin to the wood chips. Solution-based fire retardants, such as those disclosed in the Oberley ""010 patent, cannot be used to treat finished composite wood products because the products are dimensionally unstable when contacted with water. The solution can only be used to treat oriented strand board if individual chips are treated and dried before board formation. This, however, is an expensive time consuming step. It would be more efficient if the retardant could simply be mixed with the furnish during board formation.
The commercially available solid GUP/boric acid fire retardants also can only be used to treat composite wood products if dissolved, and used to individually treat the wood chips before board formation. The solids are not in an appropriate form to mix with the furnish because, as noted above, they are typically cut into 0.5-1.5 inch chunks which do not mix with the fine materials present in the composite wood furnish. Moreover, because of their structure and stickiness, the prior art solids do not flow well, and thus cannot be mixed with materials such as composite wood furnish with any level of precision. Even if they could mix well, the chunks themselves are so dishomogenous that a homogenous distribution of GUP and boric acid throughout the furnish could not be expected. In addition, GUP is very difficult to size once formed, due to its low melting point and the heat developed during the sizing or grinding operation.
It is an object of the invention, therefore, to provide improved flame retardants.
It is another object of the invention to provide superior fire retardance to wood and other cellulosic products.
It is another object of the invention to provide improved methods for preparing flame retardants.
Still another object is to provide novel flame retardant compositions that can be used in the manufacture of composite wood products, and to composite wood products produced with such compositions.
Guanylurea phosphate/boric acid compositions are provided that exhibit improved properties for the treatment of material for flame retardancy.
In one embodiment the invention provides an improved GUP/boric acid formulation that exhibits at least one of the following characteristics:
(i) greater than 95, 96, 97, 98 and preferably greater than 99 percent purity;
(ii) homogeneous distribution of GUP and boric acid in formulation;
(iii) solubility of at least 70 percent in water; and
(iv) less than 5, 2 and preferably 1 percent of a salt, such as the salt of dicyandiamide and phosphoric acid.
In a second embodiment, the GUP/boric acid composition exhibits at least two, three, or all four of these characteristics.
These GUP/boric acid fire retardants have superior purity, homogeneity, and performance characteristics. The GUP/boric acid is provided in substantially pure form, i.e. greater than 95% free of unwanted by-products and unreacted starting materials, and preferably greater than 96%, 97%, 98%, or 99% pure. The GUP and boric acid are evenly dispersed for superior fire retardance and longevity, especially in high hazard applications. The fire retardants can be liquid or solid. In solid form, they can be integrated into composite wood products, and composite wood product manufacturing processes to produce composite wood products of the present invention.
It has been discovered that by achieving linear reaction kinetics between dicyandiamide and phosphoric acid, one is able to substantially increase the yields of GUP in a GUP/boric acid fire retardant production process, and to produce a substantially pure GUP/boric acid fire retardant that does not contain any significant quantities of unwanted by-products or unreacted starting materials. These higher purity products are desired for their superior performance characteristics, and for their more efficient utilization of raw materials. Moreover, solutions produced by the process of this invention can be processed into solids in which the GUP and boric acid are substantially evenly distributed.
It has surprisingly been discovered that the higher purity solids produced by the present invention are less prone to stick together during storage and handling. The stickiness of the prior art solids appears to be attributable to the hygroscopicity of by-products and unreacted residuals from the prior art GUP manufacturing processes and from the GUP itself. Because the GUP of the present invention is purer, and because the particle comprises a substantially homogenous 70:30 composition of GUP and boric acid, it is less sticky, and one is able to prepare solid compositions of particulate fire retardants that flow when subjected to gravitimetric forces. The flowability of the particles is of substantial benefit because it allows GUP and boric acid to be evenly mixed and distributed throughout the composition. It also allows batches to be subdivided without concern over the homogeneity of the batch. Flowability also allows the particles to be used in a number of applications not available to the prior art solids, such as composite wood board manufacture.
It has also been surprisingly discovered that the higher purity products of the present invention exhibit improved solubility in water. The invention provides liquid compositions of GUP/boric acid fire retardant of exceptional purity (greater than 95%, 96%, 97%, 98%, and even 99%), in which all of the retardant can be solubilized, even at concentrations greater than 70 percent fire retardant solids.
Thus, in one embodiment the invention provides solid and liquid fire retardant compositions that contain GUP and boric acid, wherein the amount of unreacted starting materials and unwanted by-products from the GUP reaction process are less than 5 wt. % of the theoretical GUP yield. The amount of such impurities is preferably less than 4% of the theoretical GUP yield, and even more preferably less than 3%, 2% or 1%. The invention also provides wood products that contain the high purity fire retardants, and methods for treating wood products with the high purity fire retardants.
The process for producing the compositions of the present invention can be exemplified by the linear plot of reaction kinetics contained in FIG. 1. These reaction kinetics should be contrasted with prior art processes which, as shown in FIG. 2, exhibit asymptotic reaction kinetics, reaching a maximum yield substantially below the theoretical yield attainable from the reaction of dicyandiamide and phosphoric acid. The present process provides a much more cost-efficient utilization of raw materials in the GUP/boric acid manufacturing process than was attained by the prior art processes, and yields a product that is much purer than the products obtained by the prior art processes.
Thus, the invention also provides a process for producing guanylurea phosphate by reacting dicyandiamide and phosphoric acid under conditions that yield substantially linear reaction kinetics. The reaction is preferably allowed to proceed to at least 95% completion, even more preferably to at least 96% or 97% completion, and still even more preferably to at least 98% or 99% completion. The reaction preferably takes place in an aqueous medium.
In one embodiment, the linear reaction kinetics are attained by dissolving in water, substantially simultaneously, dicyandiamide, phosphoric acid, and boric acid, and reacting at least a portion of the dicyandiamide and the phosphoric acid to form guanylurea phosphate, thereby forming a reaction product solution containing dissolved GUP and dissolved boric acid. The reaction is preferably run by heating the mixture once all three ingredients have been mixed, but not heating the mixture so high as to cause an exotherm, which could cause significant evaporation of the mixture and cause unwanted precipitation of solids.
The invention also provides solid fire retardant compositions in which GUP and boric acid are uniformly dispersed. In one embodiment, the solid composition is a solid particulate that contains both GUP and boric acid. In contrast to the solid compositions that are sold commercially in the prior art, in which large GUP chunks were mechanically added to boric acid solids in super sacks, the present invention provides individual solid particulates in which the GUP and boric acid are uniformly distributed. These homogenous solid compositions are particularly useful in the treatment of wood products, and especially the preparation of OSB and other composite wood products, because of the ease with which they can be mixed with the composite wood furnish, and the homogeneity of the GUP and boric acid that results within the wood product eventually produced. They can also be mixed into an adhesive resin that is used to produce a composite wood product.
Thus, in another embodiment the invention provides a wood product that comprises GUP and boric acid of greater than 95%, 96%, 97%, 98%, or 99% purity. In another embodiment the invention provides a composite wood product such as OSB that comprises GUP and boric acid. The GUP and boric acid is preferably the high purity material that is provided in another aspect of this invention. In still another embodiment the invention provides composite wood furnish, such as wood fibers or chips, or an adhesive resin used to manufacture a composite wood product, that contains GUP and boric acid. In yet another embodiment, the invention provides processes for producing fire-resistant composite wood products by mixing the particulate flame retardant composition with the furnish or adhesive resin in a composite wood production process.
The invention also provides methods of making high purity solid GUP/boric acid fire retardants by dewatering the liquid GUP/boric acid compositions of the present invention. The solution can be dewatered by any known method for separating a solvent from its solute, including by spray drying, thin film drying, and other drying techniques used by those skilled in the art of drying high solids content solutions. A preferred method of dewatering is by spray drying. This method provides a dried product that is spherical and as a result very flowable. Moreover, the product of spray drying is uniform in composition, and dissolves quickly with less heating than conventional products. The uniform, small size of the particles produced by spray drying also allows them to be readily mixed with adhesives, or other raw material furnish used to manufacture composite materials such as OSB. Spray drying also produces particles that do not create dusting problems, because the amount of small fines from the spray drying process is minimal. Thus, the product can be made readily flowable for ease of handling.
Notably, the spray drying process can also be used to manufacture fire retardant particles from materials other than GUP/boric acid. Thus, while the spray drying is preferably carried out with GUP/boric acid fire retardants, and even more preferably carried out with the high purity GUP/boric acid fire retardants otherwise provided by this invention, in another embodiment the invention provides fire retardant particles of any suitable fire retarding composition that satisfy one or more of the physical attributes of particles produced by the spray drying process. Such physical attributes include: (1) particle sphericity, (2) uniformity of size distribution, (3) flowability, (4) small particle size (generally less than 50 microns), and (5) substantial absence of fines. The particles preferably satisfy one of the preferred retardance levels set forth herein.
Thus, in another embodiment the invention provides a fire retardant composition in the form of solid particulates, wherein the composition satisfies one or more of the following characteristics:
a) the composition comprises a plurality of flowable particulates;
b) the composition comprises a plurality of spherical particles;
c) the composition comprises a plurality of particles having a substantially narrow size distribution;
d) the composition comprises a plurality of particles having an average diameter of less than 50 microns;
e) the composition comprises a plurality of particles substantially in the absence of fines.
The composition preferably comprises GUP and boric acid, and the GUP and boric acid are preferably evenly dispersed throughout or within the particules. Moreover, the particulates can also be made from other suitable fire retardants, such as the compositions used to prepare D-Blaze, Pyrolith KD, Pyroguard, FirePro, and other commercially available fire retardants. Preferred fire retardants include ammonium phosphates, ammonium polyphosphates, guanidine phosphate, melamine phosphate, urea phosphates, GUP, phosphoric acid, dicyandiamide, ammonium sulfate, sodium, potassium, or ammonium borates, urea, boric acid, and formaldehyde.
Thus, the invention provides a GUP/boric acid fire retardant that has a high concentration of GUP, and a low concentration of by-products and unreacted residuals from the GUP manufacturing process.
The invention also provides a process for producing GUP/boric acid fire retardants that more effectively utilizes raw materials, and produces higher yields of GUP than prior manufacturing processes, and less unwanted by-products.
The invention further provides wood products impregnated with high purity GUP/boric acid fire retardants that contain low or de minimis amounts of unreacted raw materials and by-products from the GUP reaction process.
The invention also provides solutions of GUP/boric acid fire retardant that include high concentrations of fire retardant.
The invention further provides a solid GUP/boric acid fire retardant in which the GUP and boric acid are substantially evenly dispersed, preferably of high purity.
The invention also provides solid particulates of GUP/boric acid with low hygroscopicity, and which can be used in material treatment processes, including composite board manufacture where flowability of the flame retardant is desired.
The invention also provides composite wood products, and furnish used in the manufacture of composite wood products, that contain GUP/boric acid fire retardants, preferably of high purity.
The invention further provides methods of manufacturing fire retardants for use in the composite wood manufacturing industry, and provides solid particles of fire retardant that can be readily integrated into the manufacture of composite wood products.